The present invention relates to a data symbol reading device for reading coded information such as two-dimensional data symbols.
Bar codes, and associated methods and devices for coding and reading bar code information, have come to be widely used for applications such as point-of-sale (POS) systems. However, since bar codes are in a one-dimensional format, in which the coding and reading of data are based on a one dimensional arrangement of bars, such systems are limited in terms of the amount of information that can be coded and read.
Data symbols, in which a mosaic or tessellated pattern is arranged in, for example, a black and white, two-dimensional symbol, have been developed in order to hold more information. Appropriate coding and reading devices have also been developed for such data symbols. These reading devices may be largely classified into two groups: those in which an image sensing device or an area sensor, such as a CCD, is used to read the data symbol pattern in two dimensions simultaneously; and those in which a line sensor is used to perform a main scan of each line, and the reading device and data symbol are moved relative to each other in a direction perpendicular to the main scanning direction to perform sub-scanning, thereby reading in two dimensions.
Reading devices which use an image sensing device (i.e., an area sensor) do not require relative movement between the reading unit and the data symbol for sub-scanning, and are thus able to read data symbols in a shorter time.
A conventional data symbol reading device 100 is shown in FIG. 1. The data symbol reading device 100 has a casing 101. The casing 100 is formed from a grip part 102, which is gripped with the hand, a head part 103, and a housing 104. The head part 103 is formed at the front end of the grip part 102 and, contains a reading unit (not shown). The reading unit includes an image sensing device, an optical system and a light source. The optical unit uses light reflected from a data symbol 38 to form an image on the light receiving surface of the image sensing device. The data symbol reading device further includes a signal processing circuit (not shown) within the grip part 102 of the casing 101, for processing the image signals output from the image sensing device.
The housing 104 extends from the head part 103 towards the symbol reading area 36. The housing 104 has a rectangular front opening 105, which substantially coincides with the symbol reading area 36.
When the data symbol reading device 100 is used for reading, the grip part 102 is held with the hand, and the housing 104 is moved over the reference plane 107, so that the data symbol 38 is positioned within the front opening 105 of the housing 104 (i.e., the data symbol 38 is within the symbol reading area 36). A trigger button 106 is then pressed to start the reading operation. The light source is illuminated, and light reflected from the symbol reading area 36 passes through the optical system and forms an image on the light receiving surface of the image sensing device. The image signal output from the image sensing device is then processed and decoded by the signal processing circuit to obtain the data expressed by the data symbol 38.
However, decoding will not be performed correctly if the data symbol 38 protrudes outside the symbol reading area 36 in the positioning process described above, and a reading error will occur.
When a reading error occurs, the operator must determine the cause of the read error. However, the operator has no immediate or direct information about the cause of the error. Furthermore, even if the operator is notified of a positioning or other error, since the data symbol 38 is covered by the data symbol reading device 100, the operator cannot see the position of the data symbol 38. In such a case, the operator often is required to make a number of positional corrections, resulting in repeated reading errors, before the data symbol 38 is accurately read.